Bimetallic Cationic Metal–Organic Frameworks for Selective Dye Adsorption and Effective Cr2O72– Removal

Herein, we developed a strategy of rational constructing bimetallic metal–organic frameworks (MOFs) and at the same time embedding charges on backbones. Based on the Pearson’s hard/soft acid/base (HSAB) principle, soft base (azolate) and hard base (carboxylate) were simultaneously implanted in one building block for MOF construction, which can preferentially coordinate with relative soft acid Cu2+ and hard acid Zr4+ (or Hf4+), respectively. This combination during the self-assembly process not only generates robust coordination bonds but also leaves net charges at the metal clusters, presenting a method for rational design of bimetallic cationic MOFs. The obtained MOF exhibits effective adsorption and release properties selectively toward anionic dye and can also be applied outstandingly on Cr2O72– removal.